Every year, ish.
Usually I'll have an idea of what I want in my head, then I'm patient enough to wait for it 2nd hand or to come up in a sale.
Just bought a Fatty Trail frame, which I'm hoping that combined with selling the original Fatty (or bits thereof) will mean the cost of upgrading to a Bluto will be <£300 by the time I've raided the spares box.
Sometimes I'll just buy/sell stuff because something nice turns up, that's how I went from a Swift to an El-Mariachi. If a large SS Inbred 29 with carbon forks were to pop up at a good price (i.e. a fair bit less than the el-mariachi frame is worth) I'd probably buy that, not for a profit, I just like to ride different bikes and not spend too much £££ doing it (and fancy track ends).
